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Kathleen Brooks, research director at City Index Direct, said: "Utilities are under attack from investors because of proposals in the Labour manifesto to nationalise swathes of UK utility, energy and rail companies.

"We expect these companies to remain the target of the UK equity bears as we lead up to Thursday’s vote unless we see a pick-up in support for Theresa May and the Conservatives."

However, the FTSE 100 of Britain's biggest companies has been broadly unaffected by opinion polls in the lead up to the June 8 vote.

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Britain heads to the polls on June 8 for a snap general election. LIVE images as the campaign unfolds across the UK.

Experts have warned stocks could be in for nasty ride if there is an election shock.

Matthew Jennings, investment director at Fidelity International, said: "Many of Jeremy Corby's party’s manifesto pledges are specifically designed to reduce the profitability of the UK corporate sector and to capture a greater share of GDP in taxation to fund public spending.

"The market would also have to grapple with the prospect of nationalisation occurring in certain sectors.

"We should expect significant volatility in currency and equity markets as domestic and overseas investors adjust their exposures to reflect lower levels of expected corporate profitability in the UK under a Labour government."